Patent GB-408706-A (GB)
Title: Improvements in or relating to street traffic control systems
IPC: G08G1/08
Filed: 1932-10-26
Abstract: 408,706. Road signals for controlling traffic. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO., Ltd., Caxton House, Tothill Street, EDWARDS, F. A., 82, Elliscombe Road, Charlton, both in London, and STURROCK, G. S., c/o General Electric Co., Wembley, Middlesex. Oct. 26, 1932, No. 30003. [Class 118 (ii).] In a road traffic control system the timing apparatus comprises a condenser, a relay and a discharge tube connected in series, the condenser being initially charged and the periods being determined by the time taken for the charge on the condenser to leak away sufficiently to allow the discharge tube to strike and operate the relay. To enable the same timing apparatus to measure different periods, the condenser is arranged to discharge through a number of resistances and each of these resistances is tapped to allow the period to be adjusted. The invention is described as applied to a vehicleoperated system in which minimum and maximum periods are provided and in which the right of way is extended when a vehicle having the right of way crosses the road pad, the extension being inversely proportional to the speed of the vehicle. Fig. 1 illustrates the principle of the invention. A discharge tube 1, a relay 2 and a condenser 3 are connected in series across a source of current, the condenser being charged over a low resistance 6. When the timer is set in operation contact 4 changes over and condenser 3 discharges through high resistance 5. As the voltage across the condenser 3 falls, the voltage across tube 1 rises and the tube eventually strikes, energizing relay 2. The timer is shewn in Fig. 2 as applied to a vehicle-operated traffic control system. It is assumed that the right of way is on road A and a vehicle approaches along road B and operates pad DB. Relay DB energizes and locks up. No vehicle has passed along road A for some time so that QA is discharged and when DE energizes, S strikes and relay ST energizes and locks in series with relay STA. Relays CO and AM pull up, relay AM extinguishing the green lamp on road A and lighting the amber lamps. Relay RC energizes, changing over the demand relay DE and the right-of-way relay RW to road pads DA and DB respectively. Relay MG pulls up, DE releases, ST and STA fall away, LC energizes and GC pulls up. Meanwhile QC is discharging through RA and ZV-ZZ to time the amber period and when the voltage across G reaches the striking voltage, G strikes and AT pulls up followed by ATA, CO and AM release, BR falls away and AR energizes. The amber lights are thus extinquished and the signals are now Red on road A and Green on road B. The condenser QC has meanwhile been recharged through AT and when CO releases, a second discharge circuit for QC is completed through MGR and ZR-ZZ for timing the minimum green period. When this period has elapsed AT and ATA are again energized and as CO is now released, MG falls away to enable another demand to affect the system. If a vehicle now approaches along road A and operates DA, relay DE operates and locks, energizing ST and STA unless further vehicles are passing along road B. If however a vehicle on road B operates the pad DB, relay RW energizes and connects up a charging circuit for QA for the time that the vehicle is on the pad, that is, for a period inversely proportional to the speed of the vehicle. When the flow of vehicles along road B ceases, S strikes, ST and STA operate and CO and AM energize to initiate the transfer of right of way. Should there be no gap in the traffic flow, the maximum timer is used. The condenser QB is normally charged and when DE operates to register a demand for right of way, a discharge circuit is completed for QB over GR and ZD-ZK. When the maximum green period has elapsed, M strikes and MT and MTA pull up. Relay MTA inserts resistance ZL in the amber-timing circuit to increase the amber time period and connects QA to YB through which it rapidly discharges. S strikes, ST and STA operate and the right of way is taken from road B. The Amber period, the Minimum Green period and the Maximum Green period may be adjusted by regulators RA, MGR and GR respectively. In order that the Speed Timer shall operate satisfactorily, the striking voltage of S must be very slightly lower than the maximum voltage. If the voltage tends to vary however the arrangement shewn in Fig. 3 is used. In this arrangement the striking voltage is 170 volts, the maximum voltage is 190 and relay MG has an extra contact over which QA is charged to 30 volts. The voltage across S is thus 160 volts when DE operates and this voltage must rise to 170 before S strikes so that if RW is now reversed the charge on QA is increased to increase the right of way period. The invention may also be applied to fixed time cycle systems. Specification 400,340 is referred to.